Excessive manganese, in solutions containing metals, such as leach extracts, to be treated by electrolysis procedures for the recovery of the metals has caused problems of decreased current efficiencies during electrolytic recovery of the desired metal on the cathodes and manganese deposition on the anodes as well as poor physical and chemical characteristics of the metals recovered.
This problem of manganese and its build-up in the solutions and contamination of the desired metal has been overcome to some extent in electrolytic plants by employing a more "reactive" anode or by bleeding-off part of the solution for neutralization and separation of the desired metal by chemical precipitation prior to further treatment. Thus, for example, in electrolytic recovery of zinc, chemical lead anodes have been used in place of the normal lead/silver alloy anodes. Other efforts at overcoming the problems include the method of cleaning the manganese deposit from the anodes and cells more frequently which is expensive and time-consuming particularly where high levels of manganese are dissolved in the liquor. Moreover, in some of the procedures dealing with the removal of manganese, there is the undesired removal or loss of significant amounts of the metal desired to be recovered during the manganese removal step.
With particular reference to zinc recovery by electrolysis, this problem of manganese contamination of the electrodes is aggravated when the "Jarosite Process" is used in the recovery of zinc. The "Jarosite Process" is a well-known iron removal process employed subsequent to high acid leaching which can increase the recovery of zinc from roasted sulfide concentrates by the electrolytic zinc process. What transpires is that the roasted zinc concentrate is subjected to a strong sulfuric acid leach followed by treatment using, preferably, an ammonium ion to precipitate the iron to give a zinc sulfate solution free of the iron and with very little loss of the zinc. With such highly acid leaching, there is even a further solubilization of the manganese present in the roasted zinc sulfate concentrate which causes increased problems of electrode fouling and contamination of the desired zinc during electrolytic recovery of the zinc.